1. Field of the Invention
The present invention relates to an improvement in an air saw used for plate cutting work and deburring of metallic products as a kind of air tool.
2. Description of the Related Art
As shown in FIGS. 9 and 10, a general structure of an air saw 101 includes: a piston 113 slidably accommodated in a cylindrical cylinder chamber 112 arranged in a saw casing 102; a main spindle 129 passing through the piston 113 and having a back plate 130 arranged toward the rear end and a front plate 131 arranged toward the front end; and a blade-applied part 103 arranged at the front end of the main spindle 129 for attaching a saw blade 109 thereto.
Return springs 132 and 144 are respectively arranged in return-spring chambers 150 and 151, which are provided at the rear of the back plate 130 and the front of the front plate 131, respectively. Due to the return springs 132 and 144, the back plate 130 and the front plate 131 are urged toward the center of a cylinder 111, respectively. The front return-spring chamber 151 is open to the atmospheric air while the rear return-spring chamber 150 is formed to be an air-cushion chamber 149 communicating with an exhaust path 115 via a ventilation port 117. The exhaust path 115 is provided with two front and rear exhaust ports 152 and 153 controlled to open and close by the sliding of the piston 113.
Due to the pressure of air supplied from a charging path 104 via a charging port 114, the piston 113 in the cylinder chamber 112 is slid, so that the main spindle 129 reciprocates (moves back-and-forth) by alternately applying the pressure to pressure-receiving surfaces 130a and 131a of the back plate 130 and the front plate 131, so as to reciprocate the saw blade 109 attached to the blade-applied part 103.
However, in the conventional air saw 101 formed as described above, although the return-spring chamber 151 accommodating the return spring 144 urging the front plate 131 toward the center of the cylinder 111 is open to the atmospheric air, the rear return-spring chamber 150 accommodating the return spring 132 urging the back plate 130 toward the center of the cylinder 111 is formed to be the air-cushion chamber 149 communicating with the exhaust path 115 via the ventilation port 117, as described above. Therefore, the air in the cylinder chamber 112, for example, enters the air-cushion chamber 149 from the exhaust path 115 via the ventilation port 117 so as to increase the internal pressure of the air-cushion chamber 149.
Furthermore, the air entering the air-cushion chamber 149 through the clearance between the back plate 130 and the internal peripheral surface of the cylinder 111 also increases the internal pressure of the air-cushion chamber 149.
When the internal pressure of the air-cushion chamber 149 is increased in such a manner, the forces urging the main spindle 129 toward the center by the front and rear return springs 144 and 132 are off-balance because the internal pressure of the air-cushion chamber 149 is applied in addition to the elastic force of the return spring 132 from rear to the front relative to the elastic force of the return spring 144 from front to the rear.
As a result, as shown in FIG. 11, the back plate 130 extends beyond the normal advanced position to the front (to the left in the drawing), so that the pressure-receiving surface (front surface) 130a of the back plate 130 abuts the rear surface 113a of the retracting piston 113 so as to generate so-called chattering (which is a clink-clanking sound). The chattering is further liable to be generated when the supplied air pressure is increased.
Also, the chattering is generated when the saw blade is caught on an object to be cut, as shown in the phantom line in FIG. 11. That is, when the saw blade is caught on an object to be cut 154, in order to break this up, the air saw is instinctively pulled toward the operator (the right in the drawing, i.e., rear side). Thus, the back plate 130 extends beyond the normal advanced position of the reciprocating to the front, so that the pressure-receiving surface (front surface) 130a of the back plate 130 abuts the rear surface 113a of the retracting piston 113 so as to generate the chattering.
During the chattering that is the collision between the pressure-receiving surface 130a of the back plate 130 and the rear surface 113a of the retracting piston 113, since the front plate 131 integrated with the main spindle 129 advances further than normal, the return spring 144 is compressed further than a predetermined degree so as to reduce the strength of the spring because of dimensional changes. Thus, the force returning the main spindle 129 rearwardly (the right in the drawing) is reduced, so that the chattering is further more liable to be generated. There has also been a problem that part of the main spindle 129 attaching the back plate 130 is liable to break, reducing durability.
Moreover, the part fixing the saw blade 109 may be loosened or the saw blade 109 may come off because of the vibration due to the chattering, so that the work efficiency may be reduced. Furthermore, the chattering not only causes increased noise, but also increases the vibration, thereby deteriorating the work environment and the worker's health.
Additionally, when a member to be cut has a double structure with two plates, the rear plate may be cut even if it is not required to be cut. In order to avoid this, air supply is reduced, and even the stroke is reduced. However, the force driving the main spindle is extremely reduced because of reduced energy supply, which is not fit for practical use.